Macroscopic and Microscopic Grüneisen Parameters of Garnet, Olivine and Pyroxene
Measurements of thermal expansion from −100 to 700°C, heat capacity from 25 to 300°C (both at 1 atm) and compression from 1 bar to 120 kbar (at 25°C) have been carried out on samples of natural garnet (Al45Py41Gr13), olivine (Fo84Fa16) and pyroxene (En85Fs13) in a silica glass dilatometer, a differential scanning calorimeter and a diamond anvil X-ray camera of the Bassett design. It was found that, in both the orthorhombic olivine and the orthorhombic pyroxene, the directions of maximum and minimum thermal expansion and compression are  and , respectively. These observations are in agreement with the results of Kumazawa  who determined the adiabatic stiffness constants on pyroxene (En84Fs15) and who compared its elastic properties with those of olivine. Data obtained on the minerals in the present work at ambient conditions are presented in Table I, together with the calculated macroscopic Grüneisen parameters γ. Assuming that the γ’s are independent of temperature, the temperature coefficients of the bulk moduli of the three minerals have been estimated from the known temperature dependencies of their thermal expansion coefficients and heat capacities. The estimated values of ∂K/∂T are also given in Table I. In an optical diamond anvil apparatus of the Van Valkenburg type the pressure dependencies of the infrared active SiO4 tetrahedra vibrations of the three minerals have also been determined at pressures of as much as 50 kbar at 25°C.